The present disclosure is generally directed to electrically conductive adhesives. More particularly, the disclosure is directed to electrically conductive adhesives comprising an organic polymer resin and an electrically conductive polymer. Advantageously, the electrically conductive adhesives have low RF loss, and are thus suitable for use in a space radar antenna.
Electronic structures used in spacecraft and space radar antenna arrays are susceptible to the accumulation of electronic charge on the surfaces of the electronic structures. The space environment has a flux of energetic electrons from the solar wind and other sources. These electrons may penetrate spacecraft or sunshields and accumulate on the surfaces of the electronic structures as static charges. When the static charges accumulate to the extent that they become sufficiently high in voltage, they may discharge uncontrollably by arcing and cause damage to the electronic structure.
To protect against such uncontrolled discharge events, the conducting surfaces of electronic structures need to be grounded by leads extending to a common ground. Development of a suitable mechanism by which electronic elements of a space radar antenna can be grounded has, however, proven difficult. In particular, a space radar antenna is comprised of many metal radio frequency (RF) radiating elements, also referred to as patches, on lightweight foam tiles. These foam tiles with metal patches are bonded to each other and to a sunshield film for thermal protection. Each of these metal patches must be grounded to the spacecraft structure to avoid uncontrolled electrostatic discharges, which may interfere with the electronic elements of the antenna.
Prior methods to ground the metal patches have involved use of metal pins to separately ground each metal element. Use of metal pins, however, is impractical for use in space radar antenna, as they add complexity to the antenna design and are not practical for use with lightweight foam tiles.
Electrically conductive adhesives have also been used to ground the metal patches. Specifically, electrically conductive adhesives comprising conductive filler such as carbon powder, graphite, or electrically conductive ceramic or metals, have been used to bleed off static charges that build up on the metal patches resulting from exposure to the space environment. However, such electrically conductive adhesives have proven unsatisfactory for use in space radar antenna. Specifically, the solid conductive fillers present in the adhesive absorbing RF signals, resulting in high RF return and insertion loss. As a result, the antenna may not function properly. Additionally, if the electrical conductivity of the adhesive is too high, excessive current may flow between metal patches, leading to degradation in performance of circuits, or in the extreme case, shorting of circuits.
There is thus a need for an improved way to sufficiently ground floating metal patches in space radar antenna without loss of RF performance.